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Solar is wrongly perceived by some people to be an area-intensive energy generation technology requiring much more space than conventional fossil-fuel power plants.
The area of solar panel per person needed to provide all required energy is simply estimated. Typically, developed countries such as the United States, Australia and Singapore consume about 10 MWh of electricity per person per annum. This will need to double to accommodate the electrification of transport, heating, and industry. Assuming 22% efficient panels and a DC capacity factor of 17% (averaged across rooftop solar and solar farms), we arrive at a figure of 13 kW per person occupying 60 m2.
The global population is 8 billion, and thus 0.5 million square kilometers of solar panels are required for an affluent, energy-intensive world that is fully decarbonized using only photovoltaics. For perspective, this is 1% of the area devoted to agriculture (50 million km2). Regions with lower per capita energy consumption, and those with substantial wind or hydro resources, will need much smaller areas of solar panel per person.
Solar panels can be mounted on rooftops, at solar farms in conjunction with agriculture (agrivoltaics), in arid areas, on inland lakes (floating PV), and on calm maritime waters. Agrivoltaics and floating PV are growing rapidly, but from a much smaller base than more traditional rooftop or ground-mounted PV.
Agrivoltaics in combination with pasturing costs nearly the same as conventional ground-mounted PV, except that the panel rows might be more widely spaced. The farmer benefits from lease fees and the livestock benefit from shade from the panels. The solar farm company benefits from free grass control. Agrivoltaics in conjunction with cropping usually requires taller panel supports and other adaptations, which add to the cost.
The cost of floating PV is around 20% higher than that of rooftop solar, but can be similar to that of tracking, ground-mounted PV with bifacial modules. This augurs well for rapid future growth. Although the cost of floating PV is currently higher than roof and ground mounted PV, it has large potential in countries with high population density. Many countries have substantial inland reservoirs that can host large solar farms.
The potential for maritime floating PV is enormous. Indonesia’s calm, tropical inland sea has 0.7 million km2 of seascape that never has wind and waves larger than 15 m/sec and 4 m height respectively, which is sufficient for all the solar energy an affluent and fully decarbonized world will need.
The world has 1.3 TW of hydroelectricity capacity, which will be passed by global solar capacity during 2023. This comprises a mixture of run-of-river systems with small reservoirs and large storage reservoirs. Covering 100% of a hydroelectric storage lake with solar panels will typically yield much larger power capacity and annual energy than the hydroelectric system.
One of the largest hydropower plants in the world is Itaipu in Brazil, with a flooded area of 1350 km2 and an installed capacity of 14 GW. The 50-years old plant was part of the country’s foreign debt for many decades (US$63 billion – last instalment paid recently!). Due to water constraints and eutrophication, only 66 TWh of electricity was generated in 2021 (compared to a record 103 TWh in 2016). If the Itaipu lake were completely covered with PV modules, the installed capacity of this giant PV power plant would be 270 GW (nearly 20 times Itaipu’s installed capacity), and it would generate some 350 TWh of electricity per year (more than five times Itaipu’s 2021 production), accounting for over 70% of the Brazilian annual electricity consumption.
It took 10 years to build Itaipu, and another 10 years to bring it to full capacity. Fifty years after the Treaty of Itaipu was initially signed, it is the country’s largest “battery,” and solar PV on rooftops and on the ground benefit tremendously from this large baseload modulator. Brazil allowed solar PV to be connected to the grid only in 2012, and 10 years later reached an installed capacity nearly twice that of Itaipu (18 GW of rooftop PV and 8 GW of large-scale, ground-mounted PV as of February 2023).
Rooftop PV is the fastest growing segment of the global energy market. Rooftop PV is behind the energy meter and competes with retail electricity tariffs, which are typically much higher than wholesale tariffs. Households and companies provide the funding and assume the risk, which avoids the need for public debt.
In Australia, about one third of residential dwellings have rooftop PV. Continued rapid growth in rooftop PV is expected because most houses and commercial buildings will eventually install PV systems. An important trend is the repowering of earlier systems: houses upgrading PV systems from 2 kW to 4 kW to 8 kW to 15 kW each. Large-scale home storage to increase self-consumption is available in the form of electric vehicle batteries, home batteries and hot water storage tanks. Australia’s electricity grid remains highly stable despite dire predictions from a decade ago.
High photovoltaic conversion efficiency is key both to reducing prices and reducing land use. Efficiency has improved around fourfold since the 1950s. The first practical Si solar cell was presented in 1954, with an area of about 3 cm2. It was around 6% efficient (60 Wp/m2 at STC) and cost US$286/Wp, more than a thousand times the current price of large-area Si solar modules.
Nearly 70 years later, individual best-of-kind Si solar cells approach 27% efficiency, and commercially available Si solar photovoltaic modules are close to 24% efficient (240 Watts per m2). Commercial Si modules might reach 26% in 2030. Tandem cells have higher efficiency potential than Si cells. However, there are formidable technical and commercial obstacles, including unstable device efficiency. If these can be overcome, then 30% efficient tandem cells may become available. The required area of solar panel for a fully decarbonized energy intensive economy would drop from 60 m2 to 45 m2 per person.
Electricity demand in developing countries is much lower than in developed countries (Bolivia, Brazil, and Chile respectively 1.6, 2.5 and 4.1 MWh per capita per year). For many reasons, it is debatable whether and when energy consumption will reach the level of more affluent countries. Important drivers of future clean energy consumption include private vehicles, electrification of industrial heating, production of hydrogen atoms for the metals and chemical industry, and production of synthetic aviation fuels. Solar PV can be the energy source for all of this, and there are no area constraints in most countries.
Authors: Professor Andrew Blakers (ANU) and Professor Ricardo Rüther (UFSC).